<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>后盾人</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        body {
            width: 100vw;
            height: 100vh;
            display: grid;
            grid-template: 1fr/1fr;
        }

        button {
            width: 200px;
            height: 50px;
            background: #ecf0f1;
            color: #34495e;
            border: solid 1px #ddd;
            justify-self: center;
            align-self: center;
        }

        button::after {
            content: '';
            width: 3px;
            height: 3px;
            display: inline-block;
            /* box-shadow: 3px 0 0 currentColor, 9px 0 0 currentColor, 15px 0 0 currentColor; */
            animation-name: hd;
            animation-duration: 1s;
            animation-iteration-count: infinite;
        }

        @keyframes hd {
            from {
                box-shadow: none;
            }

            30% {
                box-shadow: 3px 0 0 currentColor;
            }

            60% {
                box-shadow: 3px 0 0 currentColor, 9px 0 0 currentColor;
            }

            90% {
                box-shadow: 3px 0 0 currentColor, 9px 0 0 currentColor, 15px 0 0 currentColor;
            }
        }
    </style>
</head>

<body>
    <button>提交</button>
</body>

</html>